Apparatus for grinding spherical surfaces



APPLICATION FILED JUNE 5. I918.

Patented Oct. 10, 1922.

2 SHEETS-SHEET 1.

APPLICATION FILED JUNE 5; I918- Patented Oct. 10, 1922.

2 SHEETS-SHEET 2.

Patented Get. 10, 1922.

APPARATUS FOR GRINDING SPHERICAL SURFACES.

Application filed June 5, .1918. Serial No. 238,253.

T all whom it may concern:

Be it known that I, WILLIAM TAYLOR, a subject of the King of Great Britain, residing in Leicester, England, have invented certain new and useful Improvements in Apparatus for Grinding Spherical Surfaces, of which the following is a specification.

This invention relates to a method and apparatus for grinding spherically curved surfaces, particularly the surfaces of lenses, reflectors and the like, by means of rotary abrasive laps of forms which are counterparts of the surfaces to be formed on the work.

The object of the invention is to provide a method and means for grinding such sur faces with greater accuracy and expedition than heretofore.

In the usual practice of grinding lenses and the like, the surface of the work is first ground more or less roughly to shape, either by means of coarse abrasive such as carborundum powder applied with water to the surface of a. metal lap, the counter part of the surface desired, or in other ways.

The lenses are then either singly, or in numbers cemented to a common holder, smoothground with a succession of abrasives of increasing degrees of fineness until the surface is both accurate as to curvature and so smooth as to be ready for polishing. The laps used for this smooth grinding are generally of soft cast-iron or other metal, and the abrasive is generally applied in the form of loose powder mixed with water. The abrasive rolls about somewhat loosely between the lap and the work, but, as the lap is always softer than the work, the abrasive indents the surface of the lap, which isenabled thereby to cause the particles to crush or scratch the surface of the work. The rolling of the loose abrasive and of the detritus between the surfaces of the lap and the work results, however, in wearing the lap to an extent which impairs seriously the accuracy of the latter, especially when the surface .of the work amounts to anything like a hemisphere, and especially in the earlier stages of smooth grinding, when the coarser abrasive is used. To reduce this drawback or difficulty to small proportions is one object of the present invention. It is usual in such smooth grinding operations to mount the lap on a rotary spindle and to apply the work to it by hand, for which purpose the work is mounted on a stem or handle,'by which it' may be presented to and pressed toward the lap, rotated intermittently and varied in its angular axial relation to the lap so as not only to distribute the grinding on the work but also to equalize the wear on the surface of the lap. By means of the handle the work can be periodically with-drawn as it becomes dry so that it and the lap may be cleaned from waste abrasive and detritus and charged afresh with water and abrasive.

Alternatively, the work is mounted on a rotating spindle and the lap applied to it by hand, but generally the convex member is attached to the spindle. sometimes the pressure between the lap and the work is produced mechanically, or mechanical means are used to move the work or the lap so as to vary continuously their angular axial relation.

Now according to the present invention I mount the lap and the work each upon a spindle mechanically rotated, I set the spindles with their axes inclined to one another and so that the spherical surfaces of the lap and the work are free to seat themselves together without constraint other than the constraint of an elastic feeding force 5 applied constantly in one direction, alnd preferably in that of the axis of the rotating lap, and I supply between the surfaces of the lap and the work a stream of liquid in such manner that it washes out continu- 0 ously from between the surfaces the detritus,

I may supply loose abrasive in such liquid, but preferably I embody or embed suitable abrasive in the surface of the lap in known manner. Abrasive so secure-d that it does not normally move upon thelap surface I hereinafter term a fixed abrasive.

I will describe the invention with reference to the accompanying drawing in which Figs. 1 and 2 are respectively a front elevation and a plan of one form of grinding apparatus constructed and operating according to my invention; Fig. 3 is an elevation and Fig. 4 a sectional plan showing a modi fied arrangement of part of the apparatus; Fig. 5 is an end view of the lap showing a spiral groove in its surface and Fig. 6 is a similar view of the lap showing the modified form of groove.

In the illustrated form of the apparatus, Figs. 1 and 2, a pan A for supporting the working parts and catching liquid and detritus is mounted on a suitable edestal B.

In bearings C C in a head attached to the pan, I provide a rotary hollow spindle C, which may be driven from any convenient source of power, as by a belt and pulley C Upon one end of and concentrically upon the spindle C, I attach by any convenient means a lap D having a spherically curved surface D, formed thereon, a counterpart of the surface required upon the work. This surface may be convex or concave according to requirements, and the lap may be of metal with abrasive upon or embedded in its surface, or may be of any other material suitable to hold or contain abrasive.

Through a duct E, communicating with the'ot-her end of the spindle C, and connected thereto by a sealing washer E, compressed by a spring E,, I supply to the lap D through a hole D preferably at its centre, liquid or liquid and abrasive from a convenient source of supply.

Upon a second spindle F, carried in a movable frame F 1 and inclined to the axis of the spindle G, I attach in known manner on a suitable holder F,, by means of a chuck F the work, for example the lens or lenses F F to be lapped, and previously formed approximately to the desired curvature. The movable frame F is at tached to and supported by a bar F adapted to slide freely, in the direction of the axis of spindle C in bearings F F carried by the pan A, the bearing F being open at the top and the bearing F open at the bottom, so that the bar m when the frame F and the work are withdrawn from the lap D, may be tilted up into the position shown dotted in Fig. 1, so as to facilitate examination of the work by the operator or its removal from the chuck F I prefer to set the axes of the spindle F and the bar F in a plane which is approximately vertical, as shown, and to arrange that the centre of curvature F of the work lies approximately at the point of intersection of these two axes, in which case the bearings F and F which fit the bar F somewhat loosely, may be set so that, in advancing the work toward the lap, the bearings direct the work approximately into line with the lap. I attach to an extension of the bar F beyond the bearings. a weight F which may be set adjustably on the bar so as to balance the weight of the work, the frame F and the parts associated with them. The work is then fed relatively toward the lap during a lapping operation by sliding the bar F in its bearings. preferably by elastic pressure, which may be given by pressure on the outer end of the bar F Such pressure may be produced by the operators hand or by other convenient means.

With the arrangement described, the lap and the work seat themselves together without constraint other than that of the feeding force. By feeding with elastic pressure in the direction of the axis of the lap, I reduce to a minimum the wear, and change of curvature, of the lap. It is convenient but not essential that the lap be mounted upon the fixed spindle and the work upon the movable spindle. The arrangement may be reversed and the lap may be fed toward the work.

The spindle F may be rotated from any convenient source of power by means of a band G and the pulley F attached to the spindle F, and, to permit a universal motion of the frame F and the parts associated with it, without relative constraint of the lap and the work, I may employ two guide pulleys G G round which the band G may pass vertically to and from the source of power, and horizontally to and from the pulley F the guide pulleys being carried on a horizontal axle G which is pivoted about a vertical axis G to a link G which, in turn, is pivoted on the frame of the machine about a vertical axis G Between the guide pulley axle G and the frame F,, and pivoted about the former axis, I interpose a strut G to receive the tension of the band G, the strut being at one end secured in a fork G which connects it to the axle G and at the other end having a ball G, working freely in a socket formed in the frame F,, as nearly as possible to the centre of the pulley F It will be seen that, with this arrangement, the tension of the vertical parts of the belt G is borne by the link G and that of the horizontal parts by the strut G in such manner that no constraint is put upon the frame F,, which is free to float. within limits, in any direction, or to be lifted as aforementioned.

It will be seen that the weight F,.,, being adjusted to balance the work and its supports when the work is being operated upon by the lap D, is able, when the work is withdrawn from the lap, to raise the work and support it in such raised position automatically.

The angle H between the axis of the spin angle dles C and F must be proportioned more or less according to the amount by which the surface of the work approaches a hemisphere, and may be adjustable, but I find that, in lapping approximately hemispherical surfaces, or surfaces which .somewhat exceed a hemisphere, the angle H may be fixed at about 20. Such an angular relation ensures sufficient constant change of contact between the various zones of the work and those of the lap to secure true sphericity of the surface formed on' the work. When the work surface is less than a hemisphere, the angle H may be less than 20 and be diminished accordingly.

I ma arrang the apparatusso that the between the axes of the spindles C and F can be adjustably varied. For that purpose I may, as shown in the modified arrangement. illustrated in Fig. 3, mount the s indle F,-carrying the chuck F and pulle in an arc-shaped piece or member F which is adjustably mounted in a second arc-shaped piece or member F supported by the sliding bar F The member F is so mounted that it can be moved to and fro over the member F along a circular path curved around the above mentioned center of curvature F One of the members, F or F, may be provided with T-shaped slots 1, 2,.curved as above to receive bolts 3 and 4 by' which the other or second member may be adjustably clamped to it so as to vary the angle Ht The said second member may have a curved tongue .adapted to fit in the mouth of one of the slots so as to guide the said member in -a circular path. In order to allow room for pulley F,',, the member F can be attached to the bar F by a bridge piece F fixed to the said bar.

I provide means by which, during the lapping operation, the liquid lubrlcant .is-

. suing from the centre of the lap may be made to reach all parts of the surfaces of the lap and work and wash out the-detritus. When the work consists, as'shown in Fig. 1, of a number of separate lenses cemented to the holder with spaces between the lenses, such spaces may be sufficient to effect this purpose, but if not, as in the case of lapping a single lens, then I adopt the known plan of conveying liquid lubricant to the interior of the hollow lap-carrying spindle,

and providing the lap with grooves and' perforations which communicate with the hollow spindle so that liquid lubricant can flow along the grooves, but according to this invention I so form and arrange the grooving I that the liquid is compelled to traverse substantially the whole of the grooving before being free to escape, thereby obtaining a more complete wetting of the surfaces-and washing away of the dedial grooves, or by turning a number of concentric grooves in the face of the lap and forming between each consecutive pair of grooves one or more short radial grooves, but to compel the liquid to traverse the circular grooves, I set such radial grooves alternately on opposite sides of the lap. In this way a stream or streams. of liquid can reach every-part of the work surface at least once during each revolution of the work.

- In the case of a concave lap, such as is shown in Fig. 1, I find it an advantage to taper or'flare the mouth of the lap.

The lap may be supplied, by means of the duct, with a liquid lubricant, such as water, and an abrasive such as emery or carborundum, but I prefer, for all exact work and especially for repetition work, to charge the lap with a fixed abrasive by pressing into its surface, or embodying with it, in known manner an abrasive, for example diamond dust, and to supply through the duct liquid without abrasive, so that abrasive is not normally moving between the work and the lap, and the latter retains its curvature for a far greater time.

Having thus described the nature of the said invention and the best means I know of carrying the same into practical effect, I claim v 1. Apparatus for grinding spherically curved surfaces, comprising a work holder, means for rotating the work holder about its axis, a lap having a spherically curved surface of the same radius as the surface to be formed upon the work, means for rotating the lap about its axis, and mountings for the work holder and the lap arranged to permit a relative approaching movement between the lap and the work carried on the holder, to permit free relative lateral movement of the work and lap in all directions allowing them to seat themselves together under the action of a force appli d to press them together, and to maintain the axes of the work and lap at a fixed angle to each other when the work and lap are seated together by such a force.

2. Apparatus for grinding spherically curved surfaces, comprising a work holder, means for rotating the work holder about its axis, a lap having a spherically curved surface of the same radius as the surface to be formed upon the work and containing abrasive fixed therein, means for rotating the lapabout its axis, and mountings for the work holder and the lap arranged to permit a relative approaching'movement between the lap and the work carried on the holder, to permit free relative lateral mov Ill! 'ment of the work and the lap in all directions allowing them to seat themselves together underthe action of a force applied to press them together, and to maintain th axes of the work and lap at a fixed angle to each other when the work and lap are seated together by such a force.

3. Apparatus for grinding spherically curved surfaces, comprising a work holder,

means for rotating-the work holder about its axis, a lap having a spherically curved surface of the same radius as th surface to be formed upon the work, means for rotating the lap about its axis, and mountings for the work holder and the lap arranged to maintain the lap axis fixed, to permit a relative approaching movement between the lap and the work carried on the holder in the direction of the axis of the lap, to permit free lateral movement of the work in all directions allowing it to seat itself upon the lap under the action of a force applied to press the Work holder and lap together, and to maintain the axis of the work at a fixed angle to the axis of the lap when the work is seated upon the lap by such a force.

4. Apparatus for grinding substantially hemispherical surfaces, comprising a work holding member, means for rotating the work holder about its axis, a lap having a substantially hemispherical surface of the same radius as the surface to be formed on the Work, means for rotating the lap about its axis, and mountings for the work holder and the lap arranged to permit a relative approaching movement between the lap and the work carried on the holder, to permit free relative lateral movement of the work and lap in all directions allowing them to seat themselves together under the action of a force applied to press them together, and to maintain the axes of the work and lap at an angle of about 20 to each other when the work and lap are seated together by such a force.

5. Apparatus for grinding spherically curved surfaces, comprising a work holder,

means for rotating the work holder about its axis, a lap having a spherically curved surface of the same radius as the surface to be formed upon the work, means for rotating the lap about its axis, and mountings for the Work holder and the lap arranged to maintain the axis of one of said members fixed, to permit a relative approaching movement between said members, to permit the axis of the other of said members to tip about a substantially fixed point so as to allow free relative lateral movement of the work and lap in all directions permitting them to seat themselves together under the action of a force applied to press them together, the axis of the member whose mounting permits it to tip being retained at a fixed angle to the axis of the other member by the cooperation of the restraint afi'orded by its mounting at said fixed point and the restraint afforded by its seating upon the other member.

6. Apparatus for grinding spherically curved surfaces, comprising a Work-holding member, a rotary spindle upon which said work-holding member is mounted, a spherically curved lap member, a rotary spindle upon which said lap member is mounted, and supports for said spindles arranged to set their axes at an acute angle to each other and to maintain them substantially at such angle during a grinding operation while permitting a relative approaching movement between the members, one of said supports being arranged to permit its spindle to tip freely about a point in line with the axis of the other spindle, so as to permit the surfaces of the members to. seat themselves together under the action of a force applied so as to press the members together.

7. Apparatus for grinding spherically curved surfaces, comprising a frame, a workholding member, a rotary spindle upon which said work-holding member is mounted, a lap member having a spherically curved surface, a rotary spindle upon which said lap member is mounted, a support for saidlap spindle rigidly mounted on said frame, a movable support for said Work spindle, and a guide for said work spindle support mounted uponsaid frame and positioned to set the axes of the work and lap at an acute angle to each other and to retain said axes at such angle during a grinding operation, while permitting the work holder to move toward the lap in the direction of the axis of the lap spindle, said guide being arranged to permit the work spindle support to tip freely inall directions about a point in line with the axis of the lap spindle, so as to permit the surfaces of the members to seat themselves together under the action of a force applied so as to press said members together.

8. Apparatus for grinding spherically curved surfaces, comprising a spherically curved lap having a hole, and grooving in the surface of the lap extending from said hole toward the periphery of said lap and so arranged that liquid from said hole is compelled to traverse substantially the whole of the grooving, means for rotating said lap, means for supplying liquid to the hole in said lap, a rotary work holder, and means for seating the said lap and the work in said holder together with their axes at an angle to each other in one plane.

9. Apparatus for grinding spherically curved surfaces, comprising a'spherically curved lap having a hole at its center and a series of circular grooves in its surface, a connecting duct between said hole and the inner circular groove, a connecting duct between each consecutive pair of circular In testimony whereof I have signed my grooves, said ducts being arranged altername to this specification in the presence of 10 nately on opposite sides of the lap, means for two subscribing Witnesses. rotating said lap, means for supplying liquid to the hole in said lap, a rotary work holder, WILLIAM TAYLOR and means for seating said lap and the work Witnesses: in said holder together With their axes at an THOMAS EDGLEY HUDSON,

angle in one plane. Ensm M. BENT. 

